Single element printer having a closed loop digital electronic control

ABSTRACT

A single spherical ball printing element having a plurality of print characters on its outside surface in rows and columns is selectively operated to present a single desired print character in a printing position in response to a digital electronic data input signal. In moving the ball to its selected position, the digital input data character signal is compared with a digital signal proportional to the position of the print ball. When the print ball reaches its desired position where the digital position signal corresponds with the data input signal, the ball is impacted against a printing surface to print the selected character.

Elite Anglin et a1.

1 51 Sept. 24, 1974 [541 SINGLE ELEMENT PRINTER HAVING A 3,586,953 6/1971 Markkancn 318/685 CLOSED LOOP G L ELECTRONIC 3,608,692 9/1971 Henry 178/34 X CONTROL 3,696,906 10/1972 Salto et al l97/l6 X Inventors: Noah L. Anglin; Roy Machamer, Primary Examiner Robert pulfrey both of San Jose Cahf' Assistant Examiner-Paul J. Hirsch [73] Assignee: Office Communications, Inc., Attorney, Agent, Firm--Umbah, Limbach &

Sunnyvale, Calif. Sutton 22 Filed: June 15, 1972 21 I N 2 3 2 [57] ABSTRACT 1 App 6 5 A single spherical ball printing element having a plurality of print characters on its outside surface in rows [52] US. Cl. 197/18, 197/55 and columns is selectively operated to present a single [51] int. Cl B41j 1/60, B4lj 23/04 desired print character in a printing position in re [58] Field of Search 197/52, 55, 18, 16; sponse to a digital electronic data input signal. In mov- 318/685; 178/34; 74/231 C, 216.5; 235/ll, 62 ing the ball to its selected position, the digital input I data character signal is compared with a digital signal [56] References Cited proportional to the position of the print ball. When UNITED STATES PATENTS the print ball reaches its desired position where the 2 905 302 9/1959 Hickerson 197/52 digital position signal corresponds with the data input 2:926:768 3/1960 Becker et 51:12:21:III: 197/52 Signal, the ball is impacted against 9 P g Surface 3,399,753 9/1968 Revelle 178/34 x to print the Selected character- 3,465,329 9/1969 Abel 178/34 X 7 Cl 7 D F.

3,548,993 12 1970 Behrens 197/52 x rawmg DATA IT? 205 TL PRINTER CYCLE 3 I '67 115 L READY PRINT COMMAND TO PRINT SOLENOID LOAD DATA L ORIVEggRCUITS I99 BALL J |79- I89 ROTATE 2037 ROTATION COMPARE COMMAND ROWE 161 POSITION I 209 SEQUENCE DATA COMPARATOR I GENERAT INPUT CARRIER I69 SPACE ADVANCE DECODE 185" COMMAND CIRCUITS 153 IBI" 2OI 2 BIT TILT 187T P05111011 CPMPARE TILT 00111111111011 COMMAND 13111151191010 I45 I91' I43 '5' I49 D IVE CIRCUITS I55 141 LOCK 4 r 9 T 5 COMMAND 1010c1 SOLENOID g a :25 DRIVE CIRCUITS I57 11 2%,, 2 e; 2 z o o o E57 ees ea" 29% PArzmzustm 3m "OF I FIG. 5 I// Blk MOTOR SENSOR ROTATION 5 BITS SENSOR STEPPER MOTOR S n B Z 7 R 20 m J K0 W. 2 U M I IN E L TE u S Q D D D D I I KI R 0 00 Ek Tm L N ON CN EL ICL FE O TIL T'- B L LIL 0 U A w S S C m PRINT I29- SENSOR I BIT PRINT SOLENOID PRINT SOLENOID DRIVE CIR CUITS BACKGROUND OF THE INVENTION This invention relates generally to the field of impact printers and more specifically to a technique for controlling the position of a single print element having a plurality of individual type characters thereon.

The concept of a single print element printing mechanism evolved in the late 19th century. A recent disclosure, as an example, of a single spheroidal type ball is given in US. Pat. No. 2,895,584 Hickerson et al. A large number of print characters are arranged on an outside surface of the single printing element in various rows and columns. A single print element having a plurality of characters thereon is presently used in commercial products such as the IBM SELECTRIC typewriter and teletype machines of the Teletype Corporation.

The traditional technique of selecting a given character on a single print element for printing has been done by the use of levers, cams, and linkages powered from a continuously rotating electrical motor. To select a given character on a spherical ball printing element, for instance, the ball must be mechanically rotated to the column in which the desired character exists and then tilted to the row in which the desired characterlies. Present mechanical techniques for accomplishing. this selection suffer from certain disadvantages. Continuous rotary motion of a motor is converted to a discrete position of the single print element to select a single print character. Subsequently, reciprocating motion is given the print element from the continuous rotary motion of the motor in order to cause the impact required to print the selected character. No mechanism is provided for insuring that the commanded action is properly executed, thus leading to the possibility of erroneous print character selection if the very complicated mechanical system is not working precisely. Furthermore, such machines are extremely complex mechanical assemblies of a very large number of parts.

With the development and widespread use of coded digital electronic signals for transferring specific character information along electrical circuits, these mechanical printing mechanisms were modified to receive and print such information. It was necessary to convert the discrete binary input electrical signal information into a series of mechanical control events acting upon the continuous rotation of the electrical motor shaft or associated shafts. The already complex mechanical assembly becomes further complicated when receiving binary electrical data of the characters to be printed. Discrete binary electrical information is translated onto a continuous mechanicalmotion which is then changed again to discrete mechanical positional states. This is a very complicated translation of information,

Accordingly, it is a primary object of the present invention to provide a single printing element printer that is very simple mechanically and further that is directly compatible with binary signals of printing characters and command functions.

It is another object of the present invention to provide a technique for verifying that a desired character on a single print element has been moved into printing v position before printing is actually accomplished.

It is yet another object of the present invention to provide a single print element printing mechanism capable of positioning its characters very accurately with respect to one another to form a high quality printed page.

SUMMARY OF THE INVENTION These and additional objects are accomplished by the techniques of the present invention wherein a single print element having a plurality of individual print characters thereon is selectively positioned by electromechanical elements having certain discrete mechanical states to which they are driven directly by application thereto of binary electrical signals representative of the characters to be printed by the single print element. Providing a plurality of discrete positions in the driving electromechanical elements according to the present invention has an advantage of simplicity and a more predictable result than the continuous mechanical motion that drives existing single print element mechanisms. Before the actual printing of a desired character is accomplished, an electronic feedback loop verifies that the desired character on the single print element is actually in printing position. Digital encoders detect the position of the print element and develop binary signals which are compared in a digital control circuit with the binary signal input of the character to be printed. In the case of a spherical ball as the single print element, anencoder is provided to detect the rotational position of the ball and another encoder is provided for detecting the tilted position of the ball. This feedback procedure reduces the chance that an undesired character will be printed in place of the desired character represented by the digital data input signal. The digital data input signal may be derived from a remote typewriter keyboard, a keyboard immediately adjacent the printer to form a compact office typewriter, a digital memory, a computer, and related sources.

The summary in the preceding paragraph has only briefly touched upon the broad concepts underlying the various aspects of the present invention. For additional objects, advantages and aspects of the present invention, reference should be had to the following description of a preferred embodiment thereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified perspective view of the essential components of a printer according to a preferred embodiment of the present invention;

FIG. 2 is a partially sectioned view of the printer of FIG. 1 taken across section 2-2 thereof;

' FIG. 3 is a sectional view of the printer of FIGS. 1 and 2 taken across section 3-3 thereof;

FIG. 4 is a sectional view of the printer of FIGS. 1-3 taken across section 4-4 of FIG. 3;

FIG. 5 is a portion of the printer of FIGS. l-4 taken across section 5-5 of FIGS. 2 and 3;

FIG. 6 is an overall diagram of the electrical control system for the mechanical elements of the printer shown in FIGS. l-5; and

FIG. 7 is an electrical circuit block diagram of the digital decision network block of the control system of FIG. 6;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring primarily to FIG. 1, the major large components of a preferred printer embodiment may be explained. A platen in the form of a roller 11 is designed to hold a sheet such as paper for printing thereon. A spherically shaped printing ball 13 (printing element) includes a plurality of characters arranged in rows and columns. Typically, the ball 13 will contain 22 columns of characters extending completely around the surface of the ball and have four rows between its top and bottom. The ball 13 is preferably easily removable from its driving mechanism so that it may be replaced with a ball having different characters. The ball 13 is supported by a carrier 15 which moves back and forth between side elements 17 and 19 of the machine frame for printing a complete line of characters one by one. The carrier 15 is guided by a guide shaft 21 as it moves along the roller 11, as well as by a rack 23 which is rigidly attached to the base 25 of the machine frame.

The print ball 13 is carried by a platform 27 within the carrier 15 that is rotatably attached to the shaft 21 while being permitted to slide therealong. The shaft 21 is in turn rotatably held by the machine frame at the end plates 17 and 19. A two position solenoid 29 is operably connected to the shaft 21 through a pivot connector 31 and a driving dog 33. The driving dog 33 is rigidly attached to the shaft 21. This mechanism is resiliently held so that the ball 13 is normally positioned a distance from the roller 11. However, when the solenoid 29 is energized, it moves to its second discrete position and causes the shaft 21 to rotate and impact the ball 13 against the roller 11, thus printing a character of the ball 13 that is in a printing position. The printing mechanism may be observed by noting FIG. 2 wherein the ball is in its normal position away from the roller 11 and FIG. 4 wherein the ball 13 is shown in its impacted position against the roller 11.

Referring primarily to FIGS. 1 and 2, a single electric stepper motor 35 (electromechanical element) is provided as part of the printer and is supported by a pair of frame members 37 and 39. Its drive (output) shaft 41 contains a driving gear 43 that rotates in response to the electrical energy being applied to the motor. This rotary motion is communicated by means of a toothed belt 45 to the carrier 15. The belt 45 is continuous, extending around idler gears 47 and 49 that are rotatably attached to the machine frame at opposite ends of the printing machine. Guiding and tensioning idler gears 51, 53, 55 and 57 further contact the continuous loop belt 45. (These idler gears serve to guide the belt in a path through the carrier 15).

The electric stepper motor 35 moves in discrete steps in response to binary electrical inputs. A stepper motor is a motor that moves to one discrete position for a given electrical input appropriately applied to the various motor windings. Conveniently for a printer of this type, the motor 35 is capable of moving between 48 discrete angular positions or steps. These discrete angular positions or steps are communicated by way of the belt 45 to the carrier 15.

As can best be seen from FIG. 2, movement of the belt 45 causes rotation of the print ball 13 by rotating a gear 59 relative to the ball support structure 27. This rotary motion is transmitted by a shaft through a print ball support mechanism 61 to the ball itself. This provides selection of the desired column of characters from the ball 13 to be presented in print position for striking the platen 11.

Provisions are made within the carrier 15 for controllably locking and unlocking the ball 13 for rotary motion. This mechanism can best be observed with reference to FIGS. 3 and 4. A bottom circumferential edge 63 of the hollow print ball 13 is provided with sawtooth shaped gear teeth (FIG. 2). A pawl 65 is normally resiliently urged upward for engaging a space between sawtooth gears and thus to hold the ball 13 against rotation. The pawl 65 is held by the ball support structure 61 in a non-rotatable position with respect thereto. The pawl 65 may be disengaged from the teeth on the lower edge of the ball 13 by a downward urging of an underside of a second pawl 67. The pawl 67 is formed at the end of a mechanical linkage 69 that is pivoted at a point 71 on the support frame 61 of the ball 13. A second pivotable linkage 73 is held by the carrier 15 in an operable relationship with a locking solenoid 75. When de-energized, the solenoid 75 is in a position that permits the pawl 65 to engage the teeth on the underside edge 63 of the ball 13 and thus hold (latch) it against rotatable motion. When the solenoid 75 is energized, its piston-like element 77 is driven inward of the carrier 15 which causes the linkages 73 and 69 to pivot and disengage the pawl 65 from the ball 13.

The top side of the pawl 67 engages a toothed tilt ring 79 (FIG. 4) for holding (latching) the ball 13 against tiltable movement. In order to select a row of characters, the ball 13 is permitted to tilt relative to its supporting structure 61. The tilt ring 79 is attached to the ball 13 in a manner to tilt therewith. Therefore, energization of the solenoid 75 unlocks the ball to permit both tilting and rotation thereof to select a desired print character for positioning in the printing position relative to the roller 11.

The electromechanical elements for tilting the ball 13 are carried by the carrier 15 and include a pair of solenoids 81 and 83 that each have two discrete positions, one when de-energized and a second discrete position when energized. Referring primarily to FIG. 5, the solenoid 81 includes a movable shaft 85 shown in its normal position when current is not applied thereto and in a dotted position current is applied to the solenoid 81. Similarly, a movable shaft 87 of the solenoid 83 normally rests in the position shown but moves to its dotted position when the solenoid 83 is energized. A rod 91 connects the two moving members 85 and 87 together. A flexible cable 93 is connected to the bar 91 and is operably connected at its other end to the ball 13 to cause it to tilt.

Most common print balls have four rows of print characters. Therefore, the electromechanical device of FIG. 5 for tilting the ball must have four discrete positions. This is obtained from the arrangement shown if the cable 93 is attached to the bar 91 a distance from one of the moving members 85 or 87 that is one-third of the total distance between these moving members. As can be seen from FIG. 5, a point of attachment 95 of the cable 93 will move to a position 95' when the solenoid 81 is energized and the solenoid 83 remains deenergized. Conversely, when the solenoid 83 is energized and the solenoid 81 remains de-energized, the point of attachment 95 moves to a position 95 When both solenoids 81 and 83 are energized, the point of attachment moves to a position 95". Thus, it can be seen that the four discrete positions as desired are provided by the two solenoid arrangements in direct response to a two bit binary electrical signal which define the desired tilt position of the ball 13.

The operable connection between the solenoids 81 and 83 and the ball 13 can best be seen from the view of FIG. 2. The cable 93 attached at one end to the bar 91 is attached at its other end to a partial circle pulley 97. The pulley 97 is rotatably held within the carrier 15. A spring 99 is held in tension between the pulley 97 and the frame of the carrier in order to resiliently hold the bar 91 in a normal position outward away from the face of the solenoids 81 and 83 so that energization of one or both of the solenoids causes the pulley 97 to rotate in opposition to the force exerted by the spring 99. Another cable 101 is attached to the outer edge of the pulley 97 and extends around a direction changing surface provided about the shaft 21 and thence continues on to connection with the tilt ring 79. The partial circle pulley 97 merely serves as a motion amplifier since its input motion is connected to a portion of the pulley having a smaller radius than that to which the output wire cable 101 is connected.

Translational motion of the carrier 15 along the width of the printer is also provided by the stepping motor 35. Such translational motion moves the ball 13 from one print column to another on some printing medium that is held against the roller 11. Such movement is accomplished by merely operating the stepper motor while the ball 13 is held in its locked position (locking solenoid 75 de-energized). As the belt 45 is moved against the ball rotating gear 59, the entire carrier 15 v will be translated since the gear 59 is'locked against ro-' tatable motion. This arrangement simplifies the mechanism further by using a single stepper motor for both of the functions of rotating the ball 13 and translating the carrier 15, dependent upon whether the ball is free to rotate (unlocked) or locked against rotatable mo tion, respectively.

A mechanism is provided on the underside of the carrier 15 for holding the carrier in a fixed position relative to the platen 11. This mechanism can best be seen from FIG. 2 wherein a second locking solenoid 105 is connected to move a pawl 107 into engagement with the rack 23 when energized. When the solenoid 105 is energized. the carrier is locked against movement along the rack 23. A spring 109 normally urges the pawl 107 to a position out of engagement with the rack 23. The rack 23 is additionally held a distance above the base plate 25 of the printer by a spacer 111 that extends between the frame sides 17 and 19. This spacer permits room for a guide member 113 to contact the underside of the rack 23. The guide member 113 is rigidly attached to the carrier 15. Another guide member 115 of the carrier rides along the top side of the rack 23 and a third guide member 117 contacts the backside of the spacer 111 opposite to the tooth portion of the rack 23. The carrier 15 is thus held at three points to the rack 23 and spacer 111 for rigid, positive support while still permitting the carrier to move back and forth along the rack 23. The rod 21 provides some additional support and stability for the carrier 15.

It should be noted that the teeth of the rack 23 are V-shaped sawtooth-like teeth in the same manner as the teeth on the lower edge 63 of the ball 13 and the teeth of the tilt ring 79 are V-shaped. The associated pawls for these teeth are cooperatively shaped in a manner to fit tightly therebetween. The electromechanical elements (motor 35 and solenoids 81 and 83) are therefore not the final positioning mechanism but merely move the ball and carrier to the approximate desired operation. When the locking pawls are engaged with their associated tooth members, the ball and carrier are precisely positioned in predetermined locations that are repeatable time after time. The result of this is a printed document with letters that are accurately spaced along a printed line and that are maintained level.

In order to form a closed loop control system to assure that the desired character on the ball 13 has been brought into the vacinity of the printing position prior to locking the ball 13 against rotatable and tiltable motion, position encoders are associated with the ball 13. It can be seen from the views of FIGS. 2-4 that a code plate 119 is held to rotate with the gear 59 and thus to rotate with the ball 13. A sensor 121 is held fixed onto the carrier structure 15 so that the code plate 119 (first encoder) rotates with respect thereto. The sensor 121 is any device that can emit an electrical signal proportional to the rotatable position of the code plate 119 and is preferably a device that emits such a signal in a binary form. For a typical ball 13 with 22 individual print columns, five binary bits of information need to be detected in order to emit a distinct binary electrical signal from the sensor 121 when each of the print columns is in printing position. The sensor 121 may include, for instance, five pairs of a light emitting diode or other light sources and a light sensing photodetector. The code plate 119 then includes on its lower surface areas of reflectance and non-reflectance at each of its particular positions according to the code of each posit1on.

Detection of the four distinct tilt positions of the ball 13 is most conveniently accomplished by including a code strip 123 (second encoder) on the wire 101 which thereby moves with the wire and thus with the position of the ball 13. A sensor 125 is held fixed to the carrier 15. The sensor 125 may include one or more light sources and one or more photodetectors in a manner to produce a two bit binary signal, one distinct two bit binary code for each of the four tilt positions of the ball 13. The control electronics of the printers are designed so that the printing of a character can occur only after a match is obtained between the data input character to be printed and the electrical signals from the rotation and tilt encoders. This assures that the correct character is being printed without leaving to chance whether or not a given mechanical element has executed its commanded function.

There are other sensors provided in the printer that emit a one bit binary code to indicate that certain functions have been performed. These binary signals are used by the printers control electronics to make sure that one operation has been completed before a next sequential operation is permitted to be initiated. Referring to FIG. 3, a lock encoder 127 is attached to the carrier 15. The encoder 127 preferably includes a light source and a photodetector sensor that emits a different signal when the pivoted connection piece 69 is in the ball locked position shown in FIG. 3 than when it is in the ball unlocked position. The light source of the sensor 127 may merely reflect off of the element 69 into its photodetector when the element 69 is in one position and not doing so when in its other position.

A similar sensor 129 (FIG. 1) is provided for reflection off of the dog 33 and serves to emit a signal when the solenoid 29 has operated the shaft 21 to effect printing of a selected character.

In order to determine when the step motor 35 has been moved one step, a sensor 131 is held to the printer frame by a bracket 133. A light source 135 and a photodetector 137 are part of the sensor 131 and form a gap therebetween for a code plate 139. The code plate 139 is rotatably attached to the step motor shaft 41 and contains a plurality of holes, one hole for each of the positions of the step motor 35. This may be 48 positions. Thus, as the motor 35 is stepped from one of its discrete positions to another, the light falling upon the photodetector 137 is broken and a pulse is emitted in its output.

Referring to FIG. 6, the printer control mechanism is outlined by a general block diagram wherein certain control elements described and shown with respect to FIGS. lare given the same reference characters. The position sensors 131, 121, 125, 127 and 129 are connected, respectively, with an electronic digital circuit 141 by lines 143, 145, 147, 149 and 151. The digital electronic circuit 141 enables certain mechanical motions by controlling distinct driving circuits 153, 155, 157, and 159 through lines 161, 163, 165 and 167, respectively. The drive circuit 153 provides the electrical signal necessary to operate the step motor 35 when a command signal to do so is emitted in the line 161 by the digital circuitry 141. The drive circuit 155 drives both of the tilt solenoids 81 and 83 according to the command in the line 163 from the digital circuits 141. The drive circuits 157 simultaneously operate the lock solenoids 75 and 105 so that when the ball 13 becomes unlocked and is permitted to rotate and tilt, the carrier becomes locked to the rack 23, and vice versa. The drive circuits 159 operate the print solenoid 29.

Data to be printed is applied through a line 169 from a data source 171 to the digital electronic circuit 141. The data source 171 may be, for instance, an ordinary typewriter keyboard with associated electronic circuits that emit a distinct binary signal for each character on the keyboard as well as distinct binary signals for backspace, space, tab functions, etc. Such a keyboard and electronics can be inserted physically into the printer frame shown in FIG. 1 immediately in front on the carrier and extending between the frame sides 17 and 19. Alternatively, data can be obtained from a remote source or from a memory, such as the memory used in association with a typewriter for editing typed material. In any event, certain housekeeping communication between the data source 171 and the digital control electronics circuits 141 is required. A signal in a line 173 therebetween tells the printer that a data character is ready to be printed. A signal from the digital electronic circuits 141 is passed through a line 175 to the data source 171 when the printer is ready to receive the character and this initiates transfer of the data character from the source 171 through the data line 169 to the printer.

The sequence of operation of the printer described with respect to FIGS. 1-6 may be best illustrated by considering in block diagram form (FIG. 7) the digital electronic circuit 141 of FIG. 6. At the end of each print cycle of the machine wherein a character has just been printed, the carrier 15 is advanced one position along the roller 11 to be ready to print a new character presented at the data input line 169. When in this position at the beginning of a new printing cycle, printer ready circuits 177 emit a ready signal in the line which causes a new data character to be presented in binary form at the data input 169. Simultaneously with this, the data source tells the printer ready circuits 177 through the line 173 that data is available to be printed. In response to this, the printer ready circuit 177 at the first instant of a new print cycle emits a signal in the load data line 179 that causes the new data character in the line 179 to be received and temporarily stored in the printer circuits until that particular character has been successfully printed.

Decoding circuits 181 receive the signal at the data input 169 and determines first whether the binary signal is for a print character or for a function command such as for a carrier space. If it is a space command, an appropriate command signal is developed in a line 183 and the carrier 15 is backspaced or forward spaced a number of spaces determined by the particular command signal. If the data input at the beginning of this cycle is, however, noted by the decoding circuit 181 to be a data character to be printed, the decoding circuit 181 emits a binary signal in the line 185 that represents a desired position of the ball 13 wherein the column in which the desired character exists is brought into printing position. Similarly, the decoding circuits 181 generate a signal in a line 187 which is representative of the tilt position of the ball that will bring the row in which the desired character appears into printing position. With the column and row thus specified, the single print character has been identified for printing.

Instead of merely commanding the electromechanical elements to turn and tilt the printing ball 13 according to the input data signal, two comparison circuits 189 and 191 are provided which compare the desired ball position 13 with its actual position. In the first instance of a data character printing cycle, the rotation and tilt positions of the ball 13 presented respectively in the lines 185 and 187 are temporarily stored in the comparators 189 and 191, respectively, by a load data pulse in the line 179. When the desired ball rotation position is loaded into the comparator 189, it will emit at its output 193 an error signal if the desired ball rotational position is not the same as its actual position as noted by the binary signal in the line 145 from the rotational sensor 121. Similarly, the comparator 191 will emit an error signal in its output 195 so long as the tilt position of the ball 13 as represented by the binary signal in the line 147 is different from that which has been loaded into the memory of the comparator from the data input circuit.

The error signals in the lines 193 and 195 occur instantaneously after the pulse in the load data line 179 occurs and results in loading the data into the memories of the comparators. If there is an error signal in either or both of the lines 193 and 195, a lock command digital circuit 197 emits in its output line 165 a signal to unlock the ball by energizing the locking solenoid 75 and simultaneously to lock the carrier to the frame by energizing the carrier lock solenoid 105. The carrier 15 is thus aligned in proper position and held while the correct print character is aligned on the ball 13. The ball 13 is now free to both tilt and rotate and this state remains until both error signals in the lines 193 and 195 disappear, denoting that the correct print character has been positioned for printing. At this instant, the lock command circuits 197 de-energize the lock solenoids 75 and 105 and thus again lock the ball 13 in position with the desired character ready for printing. The carrier although being free to move when the carrier lock solenoid 105 is 'de-energized will not do so for lack of any further forces thereon. However, the circuits can be modified to maintain the carrier lock solenoid 105 energized until after printing has occured, if desired.

During the period that the ball 13 is free to rotate and tilt, ball rotate command and enable circuits 199 and tilt command circuits 201 receive the error signals in the lines 193 and 195, respectively. When there is a rotational error signal in the line 193 and when the signal in the line 149 positively indicates that the ball is unlocked and free to rotate, the ball rotate command circuits 199 through a stepper motor rotate sequence generator 203 will cause the stepper motor 35 to advance one discrete rotational position. This causes the ball 13 to move in a manner that the print columns are moved one position to bring a new column of print characters in position for printing. The ball rotate command circuits 199 will then receive a pulse from the motor sensor 131 when the stepper motor 35 hasin fact stepped one position. This will cause, through the circuits 199 and 203, the stepper motor 35 to increment one further step so long as there is still an error signal in the line 193. As soon as there is a positive comparison between the desired rotational position and the actual rotational position in the circuits 189, the error in the line 193 will disappear and the ball rotate command circuits 199 will disable any further advance of the stepper motor 35.

Simultaneously with the ball 13 being rotated, the tilt command circuits 201 are causing the ball 13 to move from one of its discrete positions to another so long as there is an error signal in the line 195 and so long as it is sensed through a signal in the line 149 that the ball is in fact unlocked and free to tilt. As soon as the correct tilt position is reached, the error signal in the line 195 disappears because of a positive comparison in the comparator circuits 195 and the tilt command circuits 201 thus disable any further tilting of the ball 13. As mentioned previously, when both the rotational and tilt positions are reached, the lock command circuits 197 cause the ball 13 to be locked in the desired position.

The next event in the time sequence of events in one printing cycle of the printer is for print command circuits 205 to cause the ball to impact against the roller 11 and thus to print the character which has. been locked into printing position. This will occur as soon as the circuits 205 note from the signal in the line 149 that the ball has been locked and so long as a signal in a line 207 from the printer ready circuits 177 indicates that the machine is still in the print cycle which the ready circuits 177 initiated by emitting a load data pulse in the line 179. A signal is emitted in the line 167 from the print command circuits which causes energization of the print solenoid 29. When the print sensor 129 has detected that the ball 13 has moved to its printing position, the signal in the line 151 actuates print command circuits 207 to de-energize the print solenoid 29. The desired character locked into position has thus been printed and the ball 13 will return to its normal rest po sition while still remaining locked.

As the last event in the sequence of events in a single printing cycle, the carrier 15 is caused to advance one space relative to the platen 11 to be in position ready for the next character to be printed. Carrier advance command and enable circuits 209 cause the stepper motor to move one position and since the ball 13 is locked against rotational movement, the carrier 15 will move one position in response. Carrier advance com mand circuits 209 will initiate this action when it notes from the signal in the line 149 that the ball 13 is in fact locked in position, and immediately after noting from the signal in the line 151 that printing has occurred. Once the stepper motor 35 moves one position, the printingcycle has ended and a new cycle is ready to begin. As soon as the motor sensor 131 detects this final step of the motor 35 and if the ball remains locked as indicated by the signal in the line 149, the printer ready circuits 177 end the cycle signal in the line 207 and indicate by a signal in the line that the machine is ready to receive a new data character from the data source.

It will be noted that the carrier advance command 209 receives the space signal in the line 183 from the decoding circuit 181. If the binary coded information received in the data input 169 is not a character print command but rather a function command such as a space, the circuits 209 will cause the stepper motor to execute the space functions while the ball 13 remains locked.

The various aspects of the present invention have been described with respect to a preferred embodiment thereof, but it will be understood that the invention is entitled to protection within the full scope of the appended claims.

We claim:

' 1. For a printer with a carrier movable along a platen, said carrier having mounted thereon a single print element having a plurality of characters thereon in a twodimensional array, a system for selectively positioning a desired character for printing according to a data input signal, comprising:

means responsive to a first electrical signal for moving said printing element in one direction with respect to said carrier to a selected discrete position along one dimension of its'character array relative to a printing station, means responsive to a second electrical signal for moving said print element in another direction with respect to said carrier to a selected discrete position along a second dimension of its characterarray relative to said printing station,

means including a first encoder mounted to physically move with the print element in said one direction for developing a third electrical signal representative of the actual print element position in said one direction;

means including a second encoder mounted to physically move with the print element in said another direction for developing a fourth electrical signal representative of the actual print element position in said another direction,

means receiving siaid third and fourth electrical signals for comparison thereof with said input data signal, said comparison means emitting said first and second signals when said third and fourth signals, respectively, do not correspond to the data input signal,

cooperating mechanical latching elements on said printing element and said carrier,'said latching elements being movable between an engaged position wherein the printing element is locked to the carrier and a disengaged position wherein said printing element is free to move with respect to said carrier,

means receiving said first second signals for moving said mechanical latching elements into their engaged position when the comparison means no longer emits signals to drive said moving means and said another moving means,

means coupled to said locking means for emitting a lock signal when said mechanical latching elements are in their engaged position, and

means enabled only when said lock signal exists for causing printing of the selected character.

2. A printer responsive to desired character selection and space electronic signals, and utilizing a single printing element having a plurality of print characters arranged around at least a portion of the printing element's outside surface, comprising:

a printing sheet receiving platen,

a carrier assembly movable along the length of said platen and having a support attached to the printing element that is movable with respect to the carrier for positioning a desired character of the printing element into printing position,

means including cooperating mechanical latch elements carried by the printing element and carrier assembly for controllably locking said printing element to said carrier assembly with a desired character in printing position,

means responsive to electrical signals for operating said locking means, whereby the printing element may be selectively locked against movement or unlocked with respect to the carrier assembly,

an electromechanical element characterized by an output shaft that is movable through a plurality of discrete rotatable positions in sequence in response to electrical signal inputs,

a continuous flexible transmission belt driven only by said output shaft,

means coupling said transmission belt to the printing element for normally moving the printing element support in response to movement of the output shaft when said locking means is unlocked,

means responsive to said character selection signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically unlocked from each other, whereby movement of said output shaft causes movement of said printing element with respect to said carrier, and

means responsive to said space electronic signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically locked to each other, whereby movement of said output shaft causes movement of said carrier.

3. For a printing mechanism utilizing on a carrier assembly a single element spherical ball having a plurality of print characters on its outside surface arranged in rows and columns and further receiving desired digital character select and carrier advance electronic signals, the combination comprising:

a printer frame, a printing sheet receiving platen held by said printer frame,

said carrier assembly having a support for said printing ball that permits rotation and tilting of the printing ball with respect to the carrier to select, respectively, the desired column and row in which a desired character lies in a manner presenting the desired character in a printing position,

means including cooperating mechanical latching elements connected to the printing ball and said carrier assembly and movable into and out of engagement with each other for controllably locking said printing ball against any rotation with respect to the carrier,

means cooperatively shaped on said carrier and said frame for guiding said carrier in a path along said platen,

means on said carrier responsive to a locking electrical signal having locking and unlocking states for selectively moving said latching elements into and out of engagement, whereby the printing ball may be locked or unlocked with respect to the carrier assembly according to the state of said locking electrical signal,

an electromechanical element attached to said frame and characterized by an output shaft that is movable through a plurality of discrete rotatable positions in sequence in response to electrical signal inputs,

a continuous flexible transmission belt connected to be driven only by said output shaft,

means on said frame for guiding said belt along a path from said output shaft through said carrier assembly in its positions along said guiding means,

means coupling the transmission belt to the printing ball for normally rotating the printing ball in response to rotation of the output shaft when said locking means is unlocked,

means responsive to said character select signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically unlocked from each other, whereby movement of said output shaft causes movement of said printing ball with respect to said carrier,

means responsive to said carrier advance electronic signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically locked to each other, whereby movement of said output shaft causes movement of said carrier, and

means carried by the carrier assembly with mechanical coupling to said printing ball and responsive to said character select signals for causing said print ing ball to tilt into one of a plurality of definedpositions, whereby a desired character row is selected.

5. The printing mechanism of claim 3 which additionally comprises means including a sensor of the physical position of at least one of said mechanical latching elements for assuring that said locking means has in fact mechanically locked said ball against rotation with respect to said carrier before a space command signal is permitted to cause movement of said electromechanical motor.

6. A printer utilizing a single element spherical print ball having a plurality of characters on its outside surface arranged in rows and columns, comprising:

a printing sheet receiving platen,

a carrier assembly movable back and fourth along the length of said platen and having a support for said printing ball that permits rotation and tilting of the ball with respect to the carrier to select, respectively, the desired column and row in which a desired character lies in a manner presenting the desired character in a printing position,

means including electronic decoding circuits for receiving a binary electrical signal corresponding to a character desired to be printed, said decoding means having a first binary signal output corresponding to the rotational position of said print ball and a second binary signal output corresponding to the tilt position of said print ball which will bring the desired character into printing position,

means including a first encoderattached to physically move as the ball rotates for developing a third binary signal respresentative of the actual print ball rotational position, I

means including a second encoder attached to physically move as the ball tilts for developing a fourth binary signal representative of the sition,

means receiving said first and third binary electrical signals for comparison thereof in a manner to emit a ball rotate compare signal when the first and third binary signals are the same,

means receiving said second and fourth binary electrical signals for comparison thereof in a manner to emit a ball tilt compare signal when the second and fourth binary signals are the same,

means responsive to an absence of the ball rotate compare signal for rotating said print ball,

means responsive'to an absence of the ball tilt compare signal for tilting said print ball,

cooperatively shaped mechanical latching elements connected to the printing ball and said carrier assembly in a manner to be movable'into and out of engagement with each other, thereby to selectively lock the print ball against tilt and rotation,

means responsive to the simultaneous occurrence of said ball rotate compare signal and said ball tilt compare signal for moving said mechanical latching elements into engagement with each other,

a sensor on said carrier assembly coupled to said mechanical lock in a manner to emit a lock electrical signal only when said latching elements physically engage each other, and 1 means enabled by the existence of said lock electrical signal for impacting said print ball against said platen, thereby to print the desired character.

print balltilt po- 7. In a printer having a spherical print ball with a plurality of print characters arranged in columns and rows on its outside surface, said print ball being rotatable and tiltable to present a desired character in printing position, a method of printing on a record member comprising the steps of:

receiving in binary electrical form an input signal representing a data character desired to be printed,

generating from the input signal binary signals identifying the print ball row and column in which the desired character lies,

developing binary signals monitoring the physical row and column of the character in printing position,

electronically comparing the column input binary signal with the existing column signal of the print ball,

automatically rotating said print ball one column if its existing position column signal does not compare with the input column signal,

again electronically comparing the input column signal with a new ball rotational position column signal, and continuing the steps of advancing and comparing until a positive comparison of rotational position is achieved wherein the print ball rotation is stopped,

electronically comparing the row signal of the desired data character with the existing row signal of the print ball, said comparison occurring simultaneously with the rotational position comparison,

automatically moving said print ball through various tilt positions in sequence until a comparision is had between its row position signal and the row input binary data signal, wherein the print ball tilting is stopped, said tilting occurring simultaneously with the rotational position comparison and/or any ball rotation steps,

automatically locking said ball both rotatably and tiltably in position by a mechanical detent engagement in response to a comparison of both the rotatable and tiltable positions of the print ball with the desired data character in the input binary signal,

automatically impacting said'ball against the record member to record said print character in response to the mechanical detent locking the ball sensing that the ball has physically moved to an impact printing position,

automatically advancing said carrier one step along the record member in response to sensing physical movement of the ball to an impacting position in order to position the carrier for printing the next character, and

unlocking said ball after thecarrier is advanced so that the ball is again free to tilt and rotate, whereby a new data input character is received and the ball positioned to print it. 

1. For a printer with a carrier movable along a platen, said carrier having mounted thereon a single print element having a plurality of characters thereon in a two-dimensional array, a system for selectively positioning a desired character for printing according to a data input signal, comprising: means responsive to a first electrical signal for moving said printing element in one direction with respect to said carrier to a selected discrete position along one dimension of its character array relative to a printing station, means responsive to a second electrical signal for moving said print element in another direction with respect to said carrier to a selected discrete position along a second dimension of its character array relative to said printing station, means including a first encoder mounted to physically move with the print element in said one direction for developing a third electrical signal representative of the actual print element position in said one direction; means including a second encoder mounted to physically move with the print element in said another direction for developing a fourth electrical signal representative of the actual print element position in said another direction, means receiving siaid third and fourth electrical signals for comparison thereof with said input data signal, said comparison means emitting said first and second signals when said third and fourth signals, respectively, do not Correspond to the data input signal, cooperating mechanical latching elements on said printing element and said carrier, said latching elements being movable between an engaged position wherein the printing element is locked to the carrier and a disengaged position wherein said printing element is free to move with respect to said carrier, means receiving said first second signals for moving said mechanical latching elements into their engaged position when the comparison means no longer emits signals to drive said moving means and said another moving means, means coupled to said locking means for emitting a lock signal when said mechanical latching elements are in their engaged position, and means enabled only when said lock signal exists for causing printing of the selected character.
 2. A printer responsive to desired character selection and space electronic signals, and utilizing a single printing element having a plurality of print characters arranged around at least a portion of the printing element''s outside surface, comprising: a printing sheet receiving platen, a carrier assembly movable along the length of said platen and having a support attached to the printing element that is movable with respect to the carrier for positioning a desired character of the printing element into printing position, means including cooperating mechanical latch elements carried by the printing element and carrier assembly for controllably locking said printing element to said carrier assembly with a desired character in printing position, means responsive to electrical signals for operating said locking means, whereby the printing element may be selectively locked against movement or unlocked with respect to the carrier assembly, an electromechanical element characterized by an output shaft that is movable through a plurality of discrete rotatable positions in sequence in response to electrical signal inputs, a continuous flexible transmission belt driven only by said output shaft, means coupling said transmission belt to the printing element for normally moving the printing element support in response to movement of the output shaft when said locking means is unlocked, means responsive to said character selection signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically unlocked from each other, whereby movement of said output shaft causes movement of said printing element with respect to said carrier, and means responsive to said space electronic signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically locked to each other, whereby movement of said output shaft causes movement of said carrier.
 3. For a printing mechanism utilizing on a carrier assembly a single element spherical ball having a plurality of print characters on its outside surface arranged in rows and columns and further receiving desired digital character select and carrier advance electronic signals, the combination comprising: a printer frame, a printing sheet receiving platen held by said printer frame, said carrier assembly having a support for said printing ball that permits rotation and tilting of the printing ball with respect to the carrier to select, respectively, the desired column and row in which a desired character lies in a manner presenting the desired character in a printing position, means including cooperating mechanical latching elements connected to the printing ball and said carrier assembly and movable into and out of engagement with each other for controllably locking said printing ball against any rotation with respect to the carrier, means cooperatively shaped on said carrier and said frame for guiding said carrier in a path along said platen, means on said carrier responsive to a locking electrical signal having locking and unlocking statEs for selectively moving said latching elements into and out of engagement, whereby the printing ball may be locked or unlocked with respect to the carrier assembly according to the state of said locking electrical signal, an electromechanical element attached to said frame and characterized by an output shaft that is movable through a plurality of discrete rotatable positions in sequence in response to electrical signal inputs, a continuous flexible transmission belt connected to be driven only by said output shaft, means on said frame for guiding said belt along a path from said output shaft through said carrier assembly in its positions along said guiding means, means coupling the transmission belt to the printing ball for normally rotating the printing ball in response to rotation of the output shaft when said locking means is unlocked, means responsive to said character select signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically unlocked from each other, whereby movement of said output shaft causes movement of said printing ball with respect to said carrier, means responsive to said carrier advance electronic signals for enabling said electrical signal inputs to said electromechanical element when said mechanical latch elements are physically locked to each other, whereby movement of said output shaft causes movement of said carrier, and means carried by the carrier assembly with mechanical coupling to said printing ball and responsive to said character select signals for causing said printing ball to tilt into one of a plurality of defined positions, whereby a desired character row is selected.
 4. The printing mechanism of claim 3 wherein said continuous flexible transmission belt includes a toothed belt and additionally wherein said means coupling the transmission member to the printing ball includes a toothed gear rotatably fixed to a support shaft of said printing ball and positioned to engage teeth of said toothed belt.
 5. The printing mechanism of claim 3 which additionally comprises means including a sensor of the physical position of at least one of said mechanical latching elements for assuring that said locking means has in fact mechanically locked said ball against rotation with respect to said carrier before a space command signal is permitted to cause movement of said electromechanical motor.
 6. A printer utilizing a single element spherical print ball having a plurality of characters on its outside surface arranged in rows and columns, comprising: a printing sheet receiving platen, a carrier assembly movable back and fourth along the length of said platen and having a support for said printing ball that permits rotation and tilting of the ball with respect to the carrier to select, respectively, the desired column and row in which a desired character lies in a manner presenting the desired character in a printing position, means including electronic decoding circuits for receiving a binary electrical signal corresponding to a character desired to be printed, said decoding means having a first binary signal output corresponding to the rotational position of said print ball and a second binary signal output corresponding to the tilt position of said print ball which will bring the desired character into printing position, means including a first encoder attached to physically move as the ball rotates for developing a third binary signal respresentative of the actual print ball rotational position, means including a second encoder attached to physically move as the ball tilts for developing a fourth binary signal representative of the print ball tilt position, means receiving said first and third binary electrical signals for comparison thereof in a manner to emit a ball rotate compare signal when the first and third binary signals are the same, means receiving said second and fourth binary electrical signAls for comparison thereof in a manner to emit a ball tilt compare signal when the second and fourth binary signals are the same, means responsive to an absence of the ball rotate compare signal for rotating said print ball, means responsive to an absence of the ball tilt compare signal for tilting said print ball, cooperatively shaped mechanical latching elements connected to the printing ball and said carrier assembly in a manner to be movable into and out of engagement with each other, thereby to selectively lock the print ball against tilt and rotation, means responsive to the simultaneous occurrence of said ball rotate compare signal and said ball tilt compare signal for moving said mechanical latching elements into engagement with each other, a sensor on said carrier assembly coupled to said mechanical lock in a manner to emit a lock electrical signal only when said latching elements physically engage each other, and means enabled by the existence of said lock electrical signal for impacting said print ball against said platen, thereby to print the desired character.
 7. In a printer having a spherical print ball with a plurality of print characters arranged in columns and rows on its outside surface, said print ball being rotatable and tiltable to present a desired character in printing position, a method of printing on a record member comprising the steps of: receiving in binary electrical form an input signal representing a data character desired to be printed, generating from the input signal binary signals identifying the print ball row and column in which the desired character lies, developing binary signals monitoring the physical row and column of the character in printing position, electronically comparing the column input binary signal with the existing column signal of the print ball, automatically rotating said print ball one column if its existing position column signal does not compare with the input column signal, again electronically comparing the input column signal with a new ball rotational position column signal, and continuing the steps of advancing and comparing until a positive comparison of rotational position is achieved wherein the print ball rotation is stopped, electronically comparing the row signal of the desired data character with the existing row signal of the print ball, said comparison occurring simultaneously with the rotational position comparison, automatically moving said print ball through various tilt positions in sequence until a comparision is had between its row position signal and the row input binary data signal, wherein the print ball tilting is stopped, said tilting occurring simultaneously with the rotational position comparison and/or any ball rotation steps, automatically locking said ball both rotatably and tiltably in position by a mechanical detent engagement in response to a comparison of both the rotatable and tiltable positions of the print ball with the desired data character in the input binary signal, automatically impacting said ball against the record member to record said print character in response to the mechanical detent locking the ball sensing that the ball has physically moved to an impact printing position, automatically advancing said carrier one step along the record member in response to sensing physical movement of the ball to an impacting position in order to position the carrier for printing the next character, and unlocking said ball after the carrier is advanced so that the ball is again free to tilt and rotate, whereby a new data input character is received and the ball positioned to print it. 